Electromagnet



sept. 19, 1939. F Q MARX 2,173,212

ELECTROMAGNET Filed oct. 5, 1957 I N VENTOR.

'Hada/'lie .Mar'x Patented Sept. 19, 1939 UNITED STATES PATENT OFFICE ELE CTR-OMAGNET corporation of Ohio Application October 5, 1937, Serial No. 167,426`

1 Claim.

This invention relates to an electromagnet particularly adapted for lifting objects of relatively small magnetic metal content as compared with their weight.

An object of the invention is to provide such a magnet in which a large number of vari-directional magnetic circuits are set up through the energized electromagnet.

Another object is to provide a device of this kind in which the magnetic field is relatively shallow so that the electromagnet is particularly useful in lifting a single layer of objects from a plurality of such layers.

Another object is the production of an electromagnet of the kind described which may be produced simply and efliciently and which is designed for a maximum period of service.

These and other objects are obtained by the means described herein and illustrated in the accompanying drawing, in which:

Fig. 1 is a bottom plan View of the electromagnet of this invention, with part broken away, the broken away portions being indicated by dotted lines.

Fig. 2 is a cross sectional View taken on line 2-2 of Fig. 1.

The electromagnet of this invention, while obviously useful in many elds in which a device comprising the above mentioned characteristics is desirable, is nevertheless speciiically useful in a field wherein, up to the present, an electromagnet would have been of particular utility, that is, in the canning industry in which the handling of large numbers of cans and containers is a constant factor. The transfer of filled cans from one operation to another has heretofore been carried on manually. For example, the transfer of illled cans from a large container or crate to a moving belt whence they are carried to a subsequent labelling or packaging or other operation, has heretofore normally required two men who stand at opposite sides of the large container and lift therefrom two cans at a time, one in each hand. Under circumstances of this kind a device for handling, for example, a whole layer of the filled cans, would prove very useful.

The present invention is especially directed to uses of this kind. 1t provides for an electromagnet in which a great many magnetic circuits are set up upon energizing of the electromagnet so that the filled cans, which contain very little magnetic metal content as compared with their weight, may be handled without dropping olf of the cans, either of their own weight or because (Cl. TIS- 367) of slight frictional contacts occurring during the lifting operation. With further reference to the particular problem presented, it may be pointed out that the part of a can that actually cornes in contact with the surface of the electromagnet 5 is the double seam at either end of the can, This seam is, of course, contacted along its edge and between this edge and the end panel of the can there is a. space of about one-eighth of an inch which offers considerable reluctance to magnetic lines of force. Furthermore, it is to be remembered that a can such as those used in the packaging of foods, is made of sheet steel or iron that is tin plated. Tin being non-magnetic, the iron or steel is the only part of the material l5 that can be acted upon by the magnet. The magnetic metal in a can varies in thickness between 0.010 and 0.015 of an inch. The tin plating is about 0.002 of an inch thick. There are normally five thicknesses of metal in the double seam at either end of the can and this is substantially all of the magnetic material available to the circuits set up by the electromagnet. It would require very few ampere-turns of the magnet to saturate completely the magnetic metal in the rim of a can. The present invention overcomes this difficulty by providing, in the electromagnet, means for creating a great number of vari-directional magnetic circuits passing through the rim of the can.

It may be further explained that the electromagnet of this invention is designed to create a shallow magnetic field, that is, a field lying close to the face of the magnet. This is desirable because cans are normally disposed in layers and in order to lift a single layer only, without likewise lifting an undetermined number of subjacent cans, a shallow magnetic eld is required.

In greater detail and with reference to the drawing, the electromagnet may comprise a top plate 5 having an annular rim member 6 attached thereto as at 1. The electromagnet is preferably, for'the uses above suggested, of circular outline. The central portions of the plate 5 have 45 attached thereto, such as by the bolts 8, a number of electromagnetic cores 9 which, as shown, are disposed in parallel relationship with one another. Each core 9 is provided with the usual pole windings, indicated at I0.

The peripheral or rim portions of the plate 5 have attached thereto, such as by the bolts Il, a large number of magnetic cores l2 of smaller size than the central cores 9 and preferably disposed radially on the plate 5. These 55 cores are likewise provided with suitable pole windings, indicated at I3.

The windings of the central cores 9 are electrically connected with one another in series and the windings I3 of the peripheral cores are likewise inter-connected in series while the two groups of cores are connected together in parallel.

Each of the central and peripheral cores thus described has attached to its outer or bottom surface a pole piece or plate, the central pole plates being indicated by the numeral I4 and peripheral pole plates being indicated by the numeral I5. These plates are of the same general configuration and are disposed in substantially the same relationships as the cores with which they are associated.

It will be seen that the various pole plates are formed to provide projections I6 and recesses I'I which inter-nt, in spaced relationship, with the recesses and projections of adjacent plates. The various plates are attached to their respective cores by suitable means such as the bolts I3. The poles of the electromagnet units thus provided are alternately north and south, the poles in the central part of the magnet being arranged parallel to one another. There are thus provided more ampere-turns in the rim portions of the magnet than in the central portions. Furthermore, the inter-fitting or inter-locking of the pole plates makes it possible for the can rims to cross the greatest number of gaps between pole faces.

The result of the structure thus described is an electromagnet in which the greatest magnetic pull is adjacent the periphery of the magnet. In other words, the magnetic field of the magnet might be described as concave rather than conveX, as is usually the case. In this way, the outermost cans of a lifted layer, which are subject to frictional contact and bumping during the lifting operation, are held to the magnet by stronger magnetic forces than are necessary for holding the central cans on the magnet in place. The further result is achieved that the shallow magnetic eld created by the magnet is such as to preclude the picking up of more than one layer of cans from a stack oi the latter. Furthermore, the structure described provides for creating a large number of vari-directional magnetic circuits passing variously through the can rim and compensating, as it were, for the comparatively low magnetic saturation point of the cans. In this way frictional contact of the outer cans of a lifting layer, either with the container from which the cans are lifted or with other objects, does not result in displacement of these cans. Moreover, the rim 6, being of magnetic metal, serves as a shield precluding passage of electromagnetic lines of force into the walls of the crate holding the layers of cans, these crates being normally of metal.

By way of a more specic and concrete description of the electromagnetic forces produced by the magnet of this invention, reference is made to the particular embodiment shown in the accompanying drawing. Herein, each of the i8 rim coils t3 may be considered at having 63 turns and draws 40.5 amperes when connected across 110 volts D. C., in series with the remaining i7 rim coils; therefore, the ampere-turns per coil is then AT=63 40.5=2550.

Each of the 22 center section coils I0 has the same number of turns but has a greater total length of wire offering greater resistance so that on 110 volts D. C., the current is less than in the rim coils, namely, 35.5 amperes. The amperL turns are accordingly reduced: AT=63 35-5= 2236.

The magnetic density in the rim and center coils will be proportional to the ampere-turns in the rim and center coils, consequently greater in the rim coils by a percentage of 2550 divided by 2236 or 14%. The pull in each air gap of the rim is, therefore, greater than that of the center section air gap by 30% (proportional to the square of the density).

In the example under discussion the lineal length of air gap in the rim magnets (678) is less than the lineal length of the air gap of the center magnets pole faces (728) by 71/2%. This reduces the greater pull of the rim magnets from 30% to 2212%.

A further consideration is the surface area over which the total pull is distributed. The pull of the rim coils, in the example given, is exerted over an area of 527 square inches, compared with the area of the center section of 752 square inches. The pull intensity of the rim section is thereby increased relative to that oi the center section in inverse proportion to these areas, namely, 752 divided by 527 or 42.7%.

The pulling strength of the rim coils is therefore 1.225 1.427=1.748, or approximately 75% greater, per square inch of area, than that of the center section.

lt is not necessary that the cans operated upon by the electromagnet of this invention be disposed on their ends or in definite layers although it is preferable that the cans of a lifted mass be all disposed either on their sides or on their ends. The cans, however, are most ei'liciently handled when disposed on their ends in layers. The cans forming a layer need not be in any specific ordered arrangement.

For attaching the electromagnet to the lifting mechanism, the top plate 5 may have secured therein suitable attachment means such as the bolts I9 shown in Fig. 2.

Modifications will become apparent upon consideration of the means disclosed herein, but these are believed to be comprised within the spirit and scope of the present invention.

What is claimed is:

An electromagnet particularly adapted to lift a single layer of relatively small objects of low magnetic metal content from a container holding two or more of such layers and in which lifting operation the outermost of the lifted objects would tend to be displaced by contact with the container, the electromagnet being formed with a central portion comprising relatively large pole pieces and an outer portion comprising a greater' number of relatively small, adjacently-disposed pole pieces, an individual core and winding for each pole piece in said central and outer portions, the individual windings being designed and connected to provide equal ampere turn magnetization for each of the central pole pieces, and equal but somewhat larger ampere-turn magnetization for each of the outer pole pieces, to create a shallow magnetic iield providing a greater flux density in said outer portion than in said central portion, said pole pieces being adapted to pass a relatively greater number of magnetic circuits per unit area of the electromagnet working lace through objects held by said outer portion of the electromagnet than through objects held by said central portion.

FREDERICK C. MARX. 

